Solar powered heat pump construction

ABSTRACT

Disclosed is a solar powered heat pump useful for both heating and cooling building space and for providing refrigeration. The device operates on a chemical effect (adsorption) intermittent heat pump cycle in which the moderately high temperature heat generated by insolation is used to drive the desorber. The device has inherent thermal storage, can be factory built, sealed, and tested, can be electronically controlled for completely automatic operation, and includes a built-in back-up heater which obviates the need for installation of a separate back-up heating system. It can be manufactured from inexpensive materials such as glass, and implodes rather than explodes on failure. 
     A preferred embodiment of the device is designed as a modular unit which can readily be combined with others of identical design to produce a solar powered battery panel for heating and cooling. This embodiment preferably comprises a tubular enclosure defining a pair of chambers separated by a valve. A first chamber is packed with silica gel (or an equivalent adsorbent material) arranged such that mass and heat transfer through the gel take place rapidly and in comparable time periods. The first chamber is surrounded by a larger diameter, solar radiation transparent housing and the annular space between the chamber and housing is evacuated. The enclosure is mounted together with a diffuse light reflector which focuses sunlight toward the first chamber. Heat exchangers provide thermal communication between respective chambers and a pair of duct portions adapted for connection to a building heat distribution system.

BACKGROUND OF THE INVENTION

This invention relates to a novel heat pump/refrigeration system, whichuses solar energy as its primary energy source and is capable ofproviding the space heating and cooling requirements of a building.

The concepts of using the moderately "warm" heat (approximately 200°F.+), which solar collectors can provide, to heat space and to operateabsorption refrigeration units for air conditioning or refrigeration areknown. In the main, attempts to exploit these concepts have used thesolar collector merely to provide the energy needed to operateconventional heating and cooling equipment. In particular, solar heatinghas been carried out either by direct transfer of heat from a solarcollector to the space to be heated via conventional pipes or ducts, orby using the solar heat to provide moderately "warm" heat to assist theevaporator of an otherwise conventional vapor compression heat pump (thesolar assisted heat pump). During the last thirty years, solar coolinghas relied primarily upon the concept of using solar heat as the energysupply for conventional (steady state) absorption air conditioningunits.

In the known solar heating/cooling systems, it has been necessary toprovide thermal storage in a separate facility, typically as sensibleheat stored in a water tank or the like. Also, the solar energy has beenemployed merely to replace or supplement the energy normally generatedin conventional heating plants or used to power cooling equipment. Thetypical solar powered system has thus been rather costly because it hasincluded all of the components of conventional heating and coolingsystems plus solar collectors, a thermal storage facility, and specialcontrols. In addition, it has been necessary to install standby heatingand cooling capacity to provide for periods of low insolation. This ingeneral requires additional investment in conventional equipment, e.g.,an additional furnace or a greatly oversized heat pump. It also requiresthat one have a secure conventional energy supply during periods of lowinsolation. Thus, utility connections must be maintained at a capacitysufficient to provide all the required services independently of thesolar powered system. These requirements place solar energy at adisadvantage as compared with conventional energy forms, even at thecurrent high prices of energy.

Certain aspects of the design of conventional systems are awkward. Forexample, whereas the supply of solar energy is inherently intermittent,all conventional heating and cooling equipment, epecially vaporcompression heat pumps and absorption air conditioners, are designed tooperate on energy supplies which can be drawn upon continuously (e.g.electricity, gas). This however is not born of necessity, but ofconvenience. Thus, primitive "chemical effect" refrigeration machines(i.e., refrigeration devices in which chemical effects are exploited toreplace the mechanical work required in vapor compression units) thatoperated on an intermittent cycle were replaced in the marketplace bysteady state devices such as vapor compression refrigerators or airconditioners and chemical effect machines utilizing cycles such as thesteady state ammonia absorption cycle. These latter devices could beoperated continuously and were better adapted for use with the controlsthen available. Examples of intermittant cycle chemical effect devicesare disclosed in U.S. Pat. Nos. 1,873,390; 1,910,970; 1,936,039;2,138,686; 2,622,413; and 3,270,512.

Prior to 1940, a number of refrigeration devices using intermittentchemical effect refrigeration cycles similar to those described in theabove-noted patents were produced and marketed commercially. The mostfamous intermittent refrigerator to have been marketed in the UnitedStates was the "Icyball" unit. This device consisted of a closed systemhaving a pair of generally spherical chambers connected by a U-shapedtube, and containing an absorbent/absorbate pair, i.e., a refrigerantsuch as ammonia (absorbate) and water (absorbent). To use the Icyballunit, one heated the generator ball, which contained a concentratedammonia solution, to drive off an ammonia rich vapor which migrated toand condensed in the condenser ball. The unit was then placed such thatthe condenser ball was in an ice chest and the generator ball wasoutside. As the water in the generator ball cooled, its affinity forammonia greatly increased (ammonia vapor pressure decreased), andcondensed ammonia boiled, extracting heat from the ice chest, and wasabsorbed in the solution contained in the generator ball. After therefrigerant had been reabsorbed, the "weak liquor" remaining in thecondensor ball was drained to the generator ball, and the cycle could berepeated. The tube connecting the two chambers of the Icyball unit hadan orifice which constrained the flow of vapor back to the generatorball during the reabsorption (refrigeration) phase of the cycle. Thisprolonged the refrigeration cycle.

Technological development of intermittent cycle refrigeration machineshas been largely stagnant for almost forty years. However, intermittentmachines are generally much simpler and less expensive than steady statemachines, and since solar energy is inherently an intermittent energysupply, an intermittent machine powered by the sun should not be at acompetitive disadvantage with a machine designed for steady stateoperation.

Waste heat generated by industrial processes has been used to power airconditioning and refrigeration systems which operate on both absorptioncycles employing a liquid absorbent material and adsorption cyclesemploying a solid adsorbent. While these cycles operate in afundamentally identical manner, with the former it is necessary at somepoint to pump residual liquid absorbent back to the chamber in thesystem where desorption takes place. This step is not required in thelatter type of cycle since the absorbents are typically nonvolatilematerials such as silica gel, charcoal, or the like.

SUMMARY OF THE INVENTION

In its broadest aspects, the instant invention comprises a heat and masstransfer promoting structure for use in a heat pump apparatus poweredprimarily by solar radiation for heating and/or cooling a thermal sinksuch as space in a building. The apparatus is operable to exploit anintermittent heat pump cycle employing an adsorbent material and aworking refrigerant comprising a condensible adsorbate. During thecycle, refrigerant is adsorbed onto and desorbed off of the adsorbentmaterial, and heat is transferred between the adsorbent and the exteriorof the apparatus.

The apparatus comprises first and second sealed chambers separated by avalve which, when open, provides a refrigerant vapor transfer pathbetween the chambers. The first chamber contains the adsorbent materialand is in thermal communication with a solar collector. Also, the firstchamber is serviced by a first heat exchanger comprising a closed loopfor circulating heat carrying fluid through the adsorbent material sothat heat can be exchanged between the adsorbent material and airexterior thereto. Similarly, the second chamber is serviced by a secondheat exchanger for exchanging heat with refrigerant contained therein.

To promote heat and mass transfer within the first chamber, theadsorbent material is distributed as a plurality of discrete wafers,each of which comprises a shaped adsorbent material having a surfaceexposed to a vapor flow path within the chamber and surfaces bounded bysheets of material of high thermal conductance. Each of the thermallyconductive sheets is in contact with the closed loop heat exchanger.When employing an adsorbent material having a thermal diffusivity α ft²/hr. and a vapor diffusivity α_(v) ft² /hr, the wafers are preferablydimensioned such that the distance D between any point therein to asheet of the heat conducting material is no greater than √0.2α and thedistance Δ between any point within the wafer to a vapor flow path is nogreater than √0.2α_(v). Even more preferably D≦ √0.12α and Δ≦√0.033α_(v). Since D=√αt (and Δ=√α_(v) t), dimensioning the wafers inthis way means that thermal diffusion can occur in less than about 12minutes [√0.2α=√αt, t=0.2 hours=12 min.], and refrigerant vapordiffusion into and out of the adsorbent can be complete in no more thanthe same amount of time.

Proper operation of the system requires reasonable rates of mass andheat transfer through the adsorbent material selected for use in thesystem. Since vapor and thermal diffusivities through various adsorbentmaterials differ, efficient operation is promoted by designing thediscrete wafers so that thermal transfer, the rate limiting step, can becompleted rapidly. Optimally, complete mass and thermal transfer occursubstantially simultaneously. When the adsorbent/adsorbate pair issilica gel/water (α for silica gel is 84×10⁻⁴ ft² /hr. and α_(v) forwater through silica gel is 2.96 ft² /hr.) D, is preferably ≦ about 0.45inch and Δ preferably ≦ about 3.0 inch.

While a variety of operable configurations embodying the foregoingteaching will be apparent to those skilled in the art, a preferredstructure comprises a plurality of cylindrical sheet metal cans arrangedcoaxially within a tubular chamber. Each can has an outside casing whichis radially separated from the interior surface of the tube. Respectivecans are axially separated from each other. The axial dimension of thecan should be no greater than √0.2α_(v). Each can has a plurality ofsubstantially parallel sheet metal separators connected to the outsidecasing which define a plurality of wells for holding adsorbent material.The distance between the separators is no greater than 2√0.2α. When thewells are packed with adsorbent material, the annular space between theoutside casing of the cans and the inside wall of the tubular chamber,and the space between the axially separated cans comprise vapor flowpaths. The sheet metal separators are thermally conductive and are inthermal communication with the closed loop of the first heat exchanger.Mass transfer between any point in the wafer of adsorbent material to avapor flow path and heat transfer between any point in a wafer to asheet metal separator thus occur in comparable times, e.g., no greaterthan about 12 minutes.

Each of the cans has at least two cooling tube segments in contact witha sheet separator or the outside casing. The cans are placed such thatcooling tube segments in adjacent cans interfit and communicate witheach other to form a continuous conduit comprising a portion of theclosed loop heat exchanger. Further, the cooling tube segments haveaxial extensions beyond the outside casing walls to provide spacers foraxially separating the cans and radial extensions to provide radialspacers for separating the cans from the interior wall of the tubularchamber. To promote optimum solar heat absorption, the interior of thetube is coated with a high emissivity material and the exterior surfaceof the outside casing of the cans is coated with a radiation absorptivematerial.

In accordance with another aspect of the invention, a heat transferpromoting-condensate holding structure is disposed within the secondchamber where, during the cycle, refrigerant is condensed, frozen,vaporized, or sublimed. This structure comprises a plurality of discretecontainers of heat conducting material for holding nonvapor refrigerantand for promoting heat transfer therewithin. Each of the containers isopen to the interior of the chamber and is in thermal communication withthe second heat exchanger. Where the nonvapor refrigerant has a thermaldiffusivity of α_(c) ft² /hr, each container is dimensioned such thatthe distance L between a wall of the container and all pointstherewithin is no greater than √0.2α_(c), preferably no greater than√0.12α_(c).

Accordingly, it is an object of the invention to provide an improvedsolar powered heat pump apparatus utilizing an intermittent adsorptioncycle which promotes efficient heat and mass transfer in the chamberswhere thermodynamic interactions occur. Another object is to provide achamber design which can be adapted to allow the use of a wide varietyof adsorbent/adsorbate pairs in the solar powered heat pump as will berequired for different climates and different uses of the system.

These and other objects and features of the invention will be apparentfrom the following description of some preferred embodiments and fromthe drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-4 are diagrammatic illustrations useful in describing theheating cycle of the solar powered apparatus of the invention;

FIGS. 5-8 are diagrammatic illustrations similar to those of FIGS. 1-4illustrating the cooling cycle of the apparatus;

FIG. 9 is a diagram illustrating one method of storing cooling capacityduring periods of low insolation for use in providing refrigerationduring subsequent periods of intense insolation;

FIG. 10 is a diagram illustrating a method of utilizing the storedcooling capacity;

FIG. 11 illustrates an exemplary system for controlling the apparatus ofthe invention;

FIG. 12 is a graph of the mass ratio of adsorbate to dry absorbentmaterial versus temperature useful in describing the cycle employed inthe apparatus and process of the invention;

FIG. 13 is a longitudinal cross-sectional view of a modular unitembodying the apparatus of the invention capable of effecting both theheating and cooling cycles;

FIG. 14 illustrates apparatus comprising a diffuse light reflector and aplurality of the modules of FIG. 13 connected in series to a duct systemto form a solar heating/cooling panel;

FIG. 15 is a fragmentary cross-sectional view of a portion of the panelof FIG. 14 illustrating how the diffuse light reflector simulates theperformance of sun-following devices;

FIG. 16 is a partially cut-away view of a portion of the chamber of theapparatus of FIG. 13 showing a preferred structure for promoting heatand mass transfer within the adsorbent material;

FIG. 17 is a partially cut-away elevation of the chamber of FIG. 16illustrating how the structures containing the adsorbent material aremaintained in position with respect to the outer wall of the chamber andwith respect to each other;

FIG. 18 is a perspective view of a wafer of adsorbent material as itwould appear in the wells of the structure of FIGS. 16 and 17; and

FIG. 19 is a diagram illustrating how the process and apparatus of theinvention can be staged to produce low temperature refrigeration.

Like reference characters in the respective figures of the drawingindicate corresponding parts.

DESCRIPTION OF THE PREFERRED EMBODIMENT The System

Several fundamentally different types of devices for moving heat areknown in the art. These include vapor compression systems and so called"chemical effect" systems, which may be further categorized ascontinuous cycle systems or intermittent cycle systems, and asabsorption or adsorption systems. All such devices involve heattransfers with thermal reservoirs at at least three differenttemperatures: a low temperature reservoir which acts as a sink fromwhich heat is extracted, a medium temperature reservoir to which heat issupplied, and a high temperature reservoir from which heat is alsoextracted. In refrigerators and air conditioners, the low temperaturereservoir is what is cooled, and heat is dumped into the mediumtemperature reservoir. In heat pump heating systems, the mediumtemperature reservoir is what is being heated and the low temperaturereservoir is the cold outdoor air or other cold thermal sink whichsupplies the heat. When the objective is to remove heat and thereby coola given area, these devices are referred to as refrigerators or airconditioners. When the objective is to provide the heat necessary towarm an area, they typically are referred to as heat pumps. As usedherein, the term "heat pump" will refer generically to devices designedfor either purpose.

Whenever a source of heat is available having a temperature higher thanthe temperature of the reservoir of intermediate temperature into whichheat is to be moved, it is possible both in principle and practice toexploit the inherent thermodynamics of the situation to effect heatpumping, and thus to deliver more heat to the intermediate temperaturereservoir than is extracted from the highest temperature reservoir. Inchemical effect heat pumps, that is, systems wherein chemical effectssuch as absorption or adsorption replace the mechanical work done invapor compression systems, the high temperature thermal reservoirtypically comprises a boiler or a source of exhausted steam. In thedevice here under discussion, the high temperature reservoir is thesolar generated heat.

The instant invention was developed in response to the realization thatit should be possible to design an intermittent cycle heat pump devicewhich could be used for both heating and cooling and could be powered bya heat source at temperatures that can be generated within presentlyavailable solar collectors. In the heating mode, the apparatus deliversmore heat to the medium temperature reservoir than is collected frominsolation. Thus, the device can meet the heating needs of a giventhermal sink, e.g. a given building space, by drawing on a solarcollection capacity which would be unable in one day to collectsufficient heat to maintain the temperature of the building if the solarheat were simply delivered in the conventional manner. In the coolingmode, heat is extracted from a sink to be cooled such as building space(now serving as the low temperature reservoir) and dissipated into thehotter exterior environment (not functioning as the intermediatetemperature reservoir).

With "steady-state" heat pumps, heat exchange at any given point in thesystem always takes place with the same reservoir. In the intermittentmachine, the reservoirs with which given points in the system exchangeheat must be intermittently changed. Thus, intermittent cycles alwaysinclude two heat exchanges with a single point in the system: one whichremoves heat from a low temperature reservoir, and one which removesheat from a high temperature reservoir. In the apparatus disclosedherein, the switching is done using a system which directs heat carryingfluid such as air or water from the appropriate reservoir in heatexchange relation with various points in the system. Advantageously, theheat pump can be switched from a heating to a cooling mode simply byappropriately directing the fluid flow.

The discussion which follows is in the main directed to heating andcooling building space. This use of the system and apparatus of theinvention has economic significance and is a preferred application ofthis technology. However, it will be obvious to those skilled in the artthat the system may readily be adapted to heat reservoirs other thanbuilding space and to provide refrigeration, as opposed to airconditioning. The following description should accordingly not beconstrued as limiting.

The heat pump will now be described with reference to FIGS. 1-11, whichbroadly illustrate its basic nature and function. The apparatuscomprises a pair of chambers (labeled I and II) connected by a wideopening valve 10, which together comprise a sealed, pressure tightassembly. Chamber I is packed with an adsorbent material 12 such assilica gel. The sealed assembly also contains a condensible adsorbatevapor (working refrigerant) selected for its ability to readilyexothermically adsorb into the material in chamber I. Chamber I is inthermal communication with a solar energy collector or itself functionsas a solar energy collector. Preferably, Chamber I contains a nonsolarpowered backup heater 14 which is used to supplement insolation duringcloudy or severely cold weather.

Chambers I and II are each provided with a heat exchanger operable toexchange heat between the chamber and either the area to be heated orcooled (e.g., building space) or the area from which heat is extractedin the heating cycle and into which heat is dissipated in the coolingcycle. In FIGS. 1-11, for simplicity and clarity, the surface areaacross which heat exchange is effected is illustrated merely as thewalls 16 and 18, respectively, of chambers I and II. Heat exchange withair from the interior of a building is accomplished by passing the airalong duct 20, over either chamber I or II (as required), and back tothe building through duct 22. Heat exchange with air from theenvironment is accomplished by passing air through either of ducts 24and 26, over chamber I or II, and back into the environment through duct28 or duct 30. A system of baffles illustrated simply as retractablemembers 32, 34, 36 and 38 make it possible to thermally isolate chamberI and exchange heat between chamber I and either air from the buildingor from the environment. After heat exchange, the air is directed eitherback outside through duct 28 or to the interior of the building throughduct 22. Similarly, a baffle system comprising retractable memers 40,42, 44, 46 operates to thermally isolate chamber II and provides thesame degree of flexibility of heat exchange. It is preferred that theapparatus also include means to control the rate of heat exchange withchamber I. One method for accomplishing this (See items 94 and 96 ofFIG. 11) is to provide air movers that can be controlled to vary thevolume of air which is passed about the heat exchanger of chamber I.Other conventional means for controlling heat exchange will be obviousto those skilled in the art. Preferably, the apparatus also comprises abooster heater 48, which functions under certain conditions to maintainthe interior temperature of the space to be heated.

It should be noted that FIGS. 1-11 are highly schematic and are setforth in order to simplify the discussion, which follows, of theoperation of the cycles and to illustrate basic features of the system.

Chambers I and II may take any desired shape. Heat exchange with thechambers can be accomplished by various well-known techniques usingestablished technology, e.g., a closed heat transfer system forcirculating a refrigerant fluid such as a halocarbon can be employed. Avariety of different types of solar energy collectors may be used, andvarious methods of delivering heat from the collector to the interior ofthe chamber are possible. The baffle system can take any operable form.The booster and backup heaters need not necessarily comprise theillustrated electrical resistance heaters, and, in fact, may be entirelyomitted in many situations.

At the beginning of the cycle, adsorbate (refrigerant) within thetwo-chambered enclosure is adsorbed in the adsorbent material disposedin chamber I. Broadly, during the course of the cycle, the adsorbatevapor is desorbed from the adsorbent material by collected solar heatand allowed to pass through the valve into chamber II where it iscondensed. During the night, heat is provided to chamber II to vaporizethe condensate; the liberated vapor passes back through the valve 10 andis readsorbed in adsorbent material 12 until the original state of thesystem is restored.

HEATING CYCLE

FIG. 12 is a graph of the concentration of the adsorbate in theadsorbent material 12 in container I versus temperature illustratingcertain aspects of the cycle. Lines O, P, Q, R comprise constantrefrigerant vapor pressure lines (isobars) above the adsorbent material.At the beginning of the cycle (e.g., shortly after dawn), at point A,the concentration of refrigerant vapor in the adsorbent material is atits peak (A', FIG. 12) and the temperature (T₁) of the adsorbate filledabsorbent material is equal to or lower than the interior temperature ofthe building. An isolation begins, with valve 10 closed so that norefrigerant can escape chamber I, the temperature within chamber I israised to T₂ (A-B, FIG. 12). The vapor pressure of the refrigerantincreases. Next, as insolation continues, valve 10 is opened andrefrigerant vapor desorbes from adsorbent material 12, passes throughthe valve, and enters chamber II (B-C). By opening baffles 40 and 44,air from the interior of the building passes in heat exchange relationto chamber II, extracts heat of condensation from the refrigerant vaporresulting in the buildup of condensate 50, (FIGS. 2-4) and is returnedto heat the building. As long as isolation continues and somerefrigerant vapor remains adsorbed in adsorbent material 12, vapor iscontinually condensed in chamber II, and its heat of condensation isused to supply heat to the building through duct 22 (FIG. 1). Ideally,the desorption of adsorbent material 12 in chamber I is done at constantvapor pressure (B-C, in FIG. 12) for maximum thermodynamic efficiency.Such constant pressure desorption may be approached by control of valve10. Thus, during insolation, the concentration of adsorbed refrigerantsteadily decreases, and the temperature within chamber I increases toits highest point in the cycle (T₃).

In the next step of the cycle (FIG. 2 and C-D of FIG. 12), valve 10 isclosed to prevent migration of vapor from chamber II, and the adsorbentmaterial in chamber I is cooled. With baffles 34 and 38 open, heat isexchanged between air from the interior of the building and theadsorbent material. The warmed air is delivered to heat the building viaduct 22. As a result of the cooling, as shown in FIG. 12, the vaporpressure of the refrigerant above adsorbent material 12 decreases. Inaddition to the sensible heat extracted from adsorbent material 12,desorbed vapor which remains in the interstitial volume of chamber I isreadsorbed, and a certain amount of heat of adsorption is liberated anddelivered to the building.

In the next step of the cycle (FIG. 3 and D-D' of FIG. 12) with baffles40, 42, 44, and 46 closed so that chamber II is thermally isolated, andwith baffles 34 and 38 open so that heat exchange between interior spaceof the building and chamber I can be continued, valve 10 is momentarilyopened. Because of the low vapor pressure in chamber I, vapor flashdistills from the condensate in chamber II, passes through the valve 10,and is adsorbed in adsorbent material 12. The adiabatic nature of theflash evaporation results in cooling of the condensate 50 in chamber IIto a temperature well below that of the atmosphere. As vapor is adsorbedin chamber I, heat of adsorption is liberated and delivered to heat thebuilding via duct 22.

At this point in the cycle (D', FIG. 12), a mass of condensate having atemperature below the atmospheric temperature is present in chamber II,and the adsorbent material 12 in chamber I has a substantial as yetuntapped capacity to adsorb additional refrigerant vapor. Accordingly,with baffles 34, 38, 42 and 46 open, air is passed from the interior ofthe building in heat exchange relation with chamber I, warmed, anddelivered back to the building through duct 22. Air from the atmosphereenters through duct 26, circulates in a heat exchange relation withchamber II to give up heat required for vaporization the condensate 50,and exits via duct 30 back into the atmosphere. As heat of vaporizationis absorbed from exterior air, vapor migrates from chamber II throughthe valve 10 and into the adsorbent material 12 in chamber I. A smallportion of the resulting heat of adsorption is used to heat incomingvapor up to the temperature of the adsorbent material. The remainingheat of adsorption is delivered to the building. Preferably, adsorptionof liberated vapor into adsorbent material 12 during this stage of thecycle is done at constant vapor pressure as this promotes thermodynamicefficiency (Note D'-A passes along isobar in FIG. 12). This mode ofoperation can be accomplished by controlling the rate of heat exchangebetween the air and the adsorbent material in chamber I. Such controlcan be achieved by varying the area of the heat exchange surface, byvarying the quantity of air passed over a given area of heat exchangesurface per unit time, or by other well known means.

During latter portions of the cycle, e.g., as the cycle approaches pointA in FIG. 12, the temperature of the adsorbent material may fall belowthe temperature of the interior of the building in very cold weather. Inthis case, booster heater 48 is actuated to warm the air exiting theapparatus through duct 22.

QUANTITATIVE EXAMPLE OF HEATING CYCLE

For purposes of quantifying the heat transfers and capabilities of theheating cycle of the apparatus, it will be assumed that a building is tobe heated with a circulating warm air stream, that the cold air returnmay fall to 55° F. during nightime service, and that the temperature ofwarmed air used to heat the building can be reduced to 75° F. for briefperiods. The temperature of the outdoor air is assumed to fall to 25° F.during the night. The cycle starts with the temperature of the adsorbentmaterial (T₁) at 60° F. If the adsorbent/adsorbate pair used is silicagel/water, the starting vapor pressure in chamber I will be 0.01 in. Hg.and the maximum temperature attained in the adsorbent material (T₃) willbe 255° F.

During stage A-B, with valve 10 closed, collected solar energy isdelivered to the adsorbent material 12 until the vapor pressure inchamber I reaches 2.00 in.Hg, i.e., the pressure required to condensewater vapor in chamber II at a temperature of 101° F. During B-C, vapormigrating through valve 10 is condensed in chamber II at thistemperature, and the heat of vaporization is delivered to the buildingas described above.

In stage C-D, the initially 255° F. adsorbent material is cooled bybuilding air with the valve 10 closed. One object of this step is toreduce the vapor pressure in chamber I to about 0.10 in. Hg, whichpressure corresponds to the saturation pressure of ice at 18° F. Inaddition, the sensible heat stored in the adsorbent is used to heat thebuilding.

In stage C-D', flash evaporation is employed to freeze the liquid waterin chamber II and to reduce its temperature to 20° F. As thistemperature is below the triple point of ice, no liquid phase willremain in chamber II. It is possible to freeze water to this temperaturebecause of the low vapor pressure in chamber I.

Next, in process D'-A, heat is transferred from the outside atmosphere,here at 25° F., and used to vaporize the 20° F. ice in chamber II. Theheat thus absorbed in chamber II supplies the heat of sublimation of theice, and the generated vapors are readsorbed in chamber I. Their heat ofadsorption, plus the sensible heat liberated by controlled cooling ofthe gel a constant vapor pressure, is delivered to the building. As thetemperature of the gel falls below 80° F. and descends towards 60° F.(Point A along constant vapor pressure line O in FIG. 12), supplementarybooster heat may be required to prevent the temperature of the warm airentering the building from falling below 75° F.

The heat transferred to and from the system is calculated assuming thespecific heat of silica gel, with water adsorbed at a concentration X,to be:

    C.sub.p =0.23+0.5X BTU/lb.°F.

The adsorbed water vapor is assumed to have the same specific heat asice. The heat of adsorption of water vapor on silica gel is equal to1,300 BTU/lb. of water. This is an average value derived from publisheddata and represents adsorption in the range of 10% concentration orless. In process A-B and C-D, a small amount of vapor will adsorb ordesorb to fill the intersticial volume among particles of silica gel inchamber I. This mass of vapor is considered negligible here, and theseprocesses are assumed to take place at constant concentration. Heatflows for each stage of the cycle calculated on the basis of theforegoing appear in Table I set forth below.

                                      TABLE I                                     __________________________________________________________________________    Heat Transfer During the Cycle (BTU/lb. of Silica Gel, Dry Basis)             Process                                                                            Vessel I                                                                           Comment      Vessel II                                                                          Comment                                           __________________________________________________________________________    A-B  +21.08                                                                             Solar heating of                                                                           0    --                                                          silica gel from                                                               60° F. to 155° F.                                     B-C  +156.00                                                                            Solar heating of                                                                           -103.66                                                                            Condensation of                                             silica gel from   water at 101° F.                                     155° F. to 255° F.,                                                               in II, with heat                                            and desorption of of condensation                                             0.10 pound of water                                                                             delivered to the                                            per pound of gel  building                                          C-D  -22.325                                                                            Cooling of silica                                                                          0    --                                                          gel from 255° F. to                                                    160° F. with heat                                                      delivered to                                                                  building                                                            D-D' -33.96                                                                             Vapor generated in                                                                         0    Adiabatic flash                                             II absorbed in I; evaporation and                                             heat of adsorption                                                                              formation of ice                                            delivered to      at 20° F.,                                           building at 118° F.+;                                                                    saturated                                                   also sensible heat                                                            extracted from gel                                                            delivered to                                                                  building                                                            D'-A -1221.41                                                                           Vapor adsorbed in I                                                                        +100.47                                                                            Heat received                                               and heat of adsorp-                                                                             from atmosphere                                             tion given to     at 25° F.                                            building along                                                                with sensible heat                                                            extracted from gel.                                                           Chamber I cools from                                                                            --                                                          118° F. to 60° F. Below                                         80° F. supplementary                                                   heat may be required.                                               __________________________________________________________________________

From the foregoing Table it can be appreciated that the net heattransfer into the system is 283.55 BTU and that heat transfer out is282.36 BTU. These figures differ only by 0.42%, and demonstrate that theassumptions on which the calculations are based are quite reasonable.Total heat delivered to the building per pound of silica gel is 282.4BTU. Heat input from the solar collector is 177.1 BTU. Accordingly, thecoefficient of performance of this cycle is 282.4/177.1=1.59: the cycledelivers 59% more heat to the building than it collects from the sun.

As is also obvious from the foregoing, the system inherentlyincorporates the capacity for thermal storage, i.e., night-time heatingis done by extracting heat from the cold atmosphere to vaporizecondensate (or sublimate) and delivering heat of adsorption produced inchamber I to the building. The thermal sink used in conventional solarheating systems comprising a tank of water or the like is not needed. Inaddition, the system has the ability to store heat by progressivelyaccumulating condensate in vessel II during periods of mild night-timeweather. For example, if over a two-day period a sunny day and mildnight were followed by a heavily overcast day and a very cold night,condensate generated during the sunny day but not vaporized during themild night would be retained in chamber II. It would then besupplemented by additional condensate generated on the following cloudyday, and the total would be available to heat the building on thefollowing cold night. To best exploit this longer term thermal storagecapability, the quantity of adsorbent and adsorbate enclosed in thesystem should be such that a maximal winter day solar exposure isinsufficient to desorb the fully charged adsorbent material. In thiscircumstance, significant flexiblity in thermal storage is provided.

For periods when insolation is insufficient to produce enough heat tomaintain the temperature of the building, the heat necessary to desorbthe adsorbent material in chamber I can be provided in part by nonsolarpowered backup heater 14 powered, for example, electrically.

Two of the more important variations possible in the foregoing cycleinvolve the regulation of pressure and temperature via control of heattransfer so that (1) the cycle can take optimum thermodynamic advantageof the outdoor air temperature and (2) adsorption and desorption(particularly the former) can be conducted along an isobar of vaporpressure.

The first point is important because the temperature of the condensatemust be maintained below the outdoor air temperature in order tomaximize the coefficient of performance of the cycle. Obviously, theratio of the amount of heat delivered to the building to the amount ofheat collected from the sun increases as the latent heat absorbed by thecondensate or sublimate during stage D'-A is increased. For this reasonit is preferred to use a refrigerant which can be both condensed andfrozen, so that both the heat of condensation and the heat of fusion maybe utilized to heat the building. If the condensate is to be vaporizedor sublimed by receiving heat from outside air it must be colder thanthe air. The lowest temperature it can attain is dependent on the vaporpressure of the cooled adsorbent in chamber I and on controlling thevalve so that vapor is produced at substantially constant temperature.

The second point is important because operation along an isobar ofadsorption enables a closer approach to reversible operation. This, inaccordance with well known principles of thermodynamics, results inhigher efficiency.

The cycle described above is a hybrid as compared with most solar heatpump designs in that it may use booster heating in the final (D'-A)stage of the cycle. The total energy required for booster heating isquite small compared to the total heat delivered to the building. Anexact calculation of the booster energy requires somewhat detailedknowledge of the system and the ambient air temperatures. However, thebooster energy required to maintain the warm air inlet temperature at75° F. when and if the temperature in vessel II falls below 80° F.towards 60° F. has been estimated to be approximately 25 BTU/lb. ofsilica gel, or about 9.4% of the total heat delivered to the building.Assuming this small amount of energy were actually needed, it couldeasily, and relatively economically, be provided by electricalresistance heater 48.

Cooling Cycle

It is an important aspect of the instant invention that merely bymodifying certain aspects of the foregoing cycle, the apparatus can beused to provide air conditioning or moderately low temperaturerefrigeration. The manner in which this can be accomplished is describedwith reference to FIGS. 5-10.

In the first stage of the cycle (A-B), with valve 10 closed, insolationheats the refrigerant-filled adsorbent material 12. When the vaporpressure in chamber I has increased to a level where the vapor can becondensed at a temperature above the outdoor air temperature, valve 10is opened and, as insolation proceeds, refrigerant vapor passes throughthe valve, enters chamber II, and is condensed (FIG. 5). The heat ofcondensation of the refrigerant vapor is dissipated into the environmentby heat exchange with outdoor air entering through duct 26 and openbaffle 42, passing about the heat exchanger of chamber II, and exitingthrough open baffle 46 and duct 30. In the next stage of the cycle(C-D), at a time when the intensity of insolation has decreased, thevalve 10 is closed, baffles 32 and 36 are opened, and outdoor airentering through duct 24, passing about the heat exchanger of chamber I,and exiting through duct 28 cools the now desorbed adsorbent material12, thereby lowering the vapor pressure of the refrigerant in chamber I(FIG. 6).

In stage D-D' (FIG. 7), with baffles 40, 42, 44, and 46 closed so thatchamber II is thermally isolated, valve 10 is momentarily opened.Because of the low vapor pressure in chamber I, flash evaporation fromcondensate 50 occurs in chamber II, and the condensate is cooled to atemperature below the temperature which is to be maintained byrefrigeration e.g., below the interior temperature of the building. Theheat of adsorption liberated when the flashed refrigerant vapor isreadsorbed into adsorbent material 12 is dissipated into the atmosphereby heat exchange with air entering through duct 24 and open baffle 32,and exiting through open baffle 36 and duct 28.

At point D' in the cycle, the low temperature condensate 50 in chamberII represents a reservoir of cooling capacity that can be tapped at anytime to extract heat from the interior of a building, refrigeratedcompartment, or the like. Thus, air from the interior of the building isintroduced via duct 20 and open baffle 40, cooled as it gives up heat tovaporize (or sublime) cold condensate 50 in chamber II, and returned tothe interior of the building via open baffle 44 and duct 22 (FIG. 8).Heat picked up by the condensate 50 in chamber II is absorbed as heat ofvaporization. The refrigerant vapor migrates through the valve 10 and isreadsorbed into adsorbent material 12 in chamber I. Again, heat ofadsorption is dissipated into the atmosphere by heat exchange withexterior air entering via duct 24 and exiting via duct 28. When allcondensate has been evaporated from chamber II, the system must becharged by additional insolation before additional cooling can occur.

As will be apparent from the foregoing description of the cooling cycle,the stage where cooling capacity can be exploited (D'-A) cannot occursimultaneously with the insolation/desorption stage (A-B-C). Since thetime when air conditioning capacity is most needed typically fallsclosely behind the daily period of most intense insolation, it isapparent that provision must be made for delaying the exploitation ofthe cooling capacity or for enabling cooling to occur during periodsother than when the cycle is in stage D'-A depicted in FIG. 8.

While it is within the scope of the present invention to provide asingle large unit constructed in accordance with the foregoingprinciples to both heat and cool space in a building as required, thepreferred method of exploiting the process and apparatus of theinvention, at least as it applies to space heating and cooling, is toprovide relatively small devices, a plurality of which are installed tosuit the needs of a particular building and its surrounding climate.Some of the advantages of such an approach are set forth in detailbelow. One of the significant advantages is that such a modular approachprovides for flexibility in utilization of the cooling cycle. Forexample, during periods of insolation, half of the units could beundergoing the desorption stage depicted in FIG. 5 (A-B-C) and buildingup cooling capacity in the form of condensate for future use, whileremaining modules could be in stage D'-A providing air conditioning(FIG. 8). In order to prevent the adsorbent material 12 in chamber Ifrom heating up and interfering with the cycle, solar exposure would beprevented by a shield or the like or the collected solar heat would berapidly dissipated into the atmosphere. This approach would requiretwice the cooling capacity actually necessary to maintain the airconditioned temperature of the building. However, in regions wherewinters are severe, such excess capacity would already be present todeal with the winter heating requirements.

Another method of exploiting the cooling capacity is to operate thesystem in the desorption stage of the cycle only at periods of maximuminsolation, e.g., for a 4-5 hour period around noon, to run the cyclerapidly through stages C-D-D', and then to utilize the built-up coolingcapacity until the next day when insolation again becomes intense. Insituations where the largest load on the system comes from winterheating, it will be possible to satisfy summer air conditioningrequirements by these and other means.

In hotter climates where the load on the system for air conditioning insummer is greater than the heating burden during the winter months, theforegoing methods cannot be utilized unless one is willing to pay forsignificantly more cooling capacity than is actually necessary to coolthe building. In such a climate, it is preferred to utilize the coolingcapacity during the night to, for example, make ice or otherwise "storecold" to be used during subsequent periods of intense insolation. FIGS.9 and 10 schematically illustrate apparatus suitable for exploiting thisapproach.

In FIG. 9, the cycle is depicted in stage D'-A. The condensate 50, atsubfreezing temperatures, is exchanging heat via a circulating fluidflow with water 52 in reservoir 54. As heat is lost to the circulatingfluid, refrigerant vapor forms in chamber II, migrates through the valve10 into chamber I, and is adsorbed, heat of adsorption being dissipatedby heat exchange with outdoor air. As shown, reservoir 54 is enclosed ina housing 56 fitted with baffles 58, 60, 62, 64. Duct system 66, 68enables air from the interior of the building to be passed in heatexchange relation with reservoir 54 and returned. Again, variouswell-known means for optimizing heat exchange between circulating fluidsand reservoir 54 may be employed.

With this arrangement, during the night, the cooling capacity ofcondensate can be stored by making ice. As shown in FIG. 10, during thenext day when demand for air conditioning increases and heavy insolationis best used to build up more condensate 50, baffles 58, 60 are closedand baffles 62, 64 opened to exchange heat with reservoir 54. Heatabsorbed from the air is used as heat of fusion of the melting ice.Obviously, other means of storing cooling capacity known to thoseskilled in the art could be used in place of the cyclic ice formationand melting described here. Thus, the foregoing description should beregarded as merely exemplary.

Controls

A most important feature of the process and apparatus of the inventionis that it is readily amenable to being controlled so that its operationis completely automatic. Further, it is possible to control operation ofthe cycle to promote optimum efficiency. Various levels ofsophistication of control are possible. FIG. 11 depicts one possiblecontrol system which enables completely automatic operation of both theheating and cooling cycle.

The system features a control means generally designated at 70comprising an input and output (I/O) network 74, logic network 76, andmemory 78. The logic and memory can be embodied, for example, as asuitably programed microprocessor. Logic network 76 is coupled (by wayto I/O network 74) to temperature and pressure sensors 80, 82 disposedrespectively in chambers I and II, indoor air temperature sensor 84,outdoor air temperature sensors 86, 88, the heated air streamtemperature sensor 90, and thermostat 92. Logic network 76 is alsocoupled by way of I/O network 74 to valve 10, booster heater 48, backupheater 14, and baffles 32, 34, 36, 38, and 40, 42 44, 46. Lastly,network 76, through I/O network 74, is also coupled to means for varyingthe rate of heat exchange with the adsorbent material contained inchamber I, here embodied as a pair of impellers 94, 96.

In operation, when the temperature of the indoor air sensed by sensor 84is less than the temperature set at thermostat 92, control means 70initiates a heating cycle wherein, during insolation, when apredetermined threshold pressure is sensed by sensor 80, valve 10 andbaffles 40 and 44 are opened and heat is exchanged between building airand the condensing vapor in chamber II. As insolation decreases and thetemperatue and vapor pressure sensed in chamber I reached a selectedlevel, the control means 70 closes valve 10 and baffles 40 and 44, opensbaffles 34, 38, and actuates impeller 96. At that time, heat exchangeoccurs between interior air and the adsorbent material in chamber I,thus providing additional heat to the building. When, as determined onthe basis of inputs received from sensors 80, 86 and 88, the vaporpressure in chamber I has reached a predetermined level (low enough toenable cooling of the condensate in chamber II to a temperature belowthat of the outside air) control means 70 opens valve 10 intermittantly,providing progressive cooling of the condensate by flash evaporation.During this portion of the cycle, heat of adsorption is removed bypassing interior air about the heat exchange surface associated withchamber I. When the temperature within chamber II has reached a selectedlow level (as detected by sensor 82), control means 70 opens valve 10and baffles 42, 46. Outside air is then forced by a fan (not shown)about chamber II where it provides heat of vaporization for the coldcondensate. Also during this stage of the cycle, the fluctuating vaporpressure in chamber I is sensed by sensor 80, and impeller 96 isactuated in response. The rate of heat removal from chamber I is thuscontrolled so that, as adsorption continues, the vapor pressure abovethe adsorbent material remains substantially constant. If, during latterstages of the cycle, temperature sensor 90 indicates a building inputtemperature below the selected temperature input of thermostat 92, thecontrol means 70 actuates booster heater 48.

When the interior air temperature as sensed by sensor 84 is greater thanthe temperatures selected at thermostat 92, the control means 70 mayinitiate a cooling cycle. As discussed in detail above, the coolingcycle operates fundamentally identically to the heating cycle, exceptthat different baffles are opened during the various stages of thecycle, and the temperatures at which heat exchanges occur will differslightly. Thus, heat removed from the chambers is dissipated into theatmosphere rather than into indoor air, and heat of vaporization issupplied to the condensate in chamber II in the fourth stage of thecycle from indoor air or from a circulating fluid stream as depicted inFIGS. 10 and 11.

As will be obvious to those skilled in the art, other different controlscheme and levels of sophistication will be possible. Thus, it iscontemplated that short term weather forecast data could be stored in aportion of memory 78 and used to vary certain parameters in the systemin preparation, for example, for a very hot or very cold upcomingperiod. For the preferred modular approach to practicing the invention,the duct system or other fluid carrying heat transfer system ofrespective modular units are preferably connected in series so that onebaffle system serves at least several units, and a single baffle controloutput would be common to many units. Among a set of units placed suchthat their operation is functionally equivalent, a set of temperatureand pressure sensors 80 and 82 need be included only in one, as thesewould provide the control means with data representative of all theunits in the set. In regions where the cooling capacity storagetechnique illustrated in exemplary fashion in FIGS. 9 and 10 isemployed, the control means could of course be adapted to regulate thisaspect of the apparatus.

A preferred control means 70 includes a programable microprocessor soldunder the trademark SUNKEEPER, manufactured by Andover Controls. Themicroprocessor is capable of dealing with 64 independent inputs and ofoperating 32 outputs to on/off control switches. Ideally, the physicalcharacteristics of the adsorbent/adsorbate pair are stored in the memoryof the controller in parametric form (parametric representation ofadsorption data is well known). A stored control program determines theoptimal operating conditions for the device, e.g., the temperature towhich the flash evaporation is to proceed and when to stop vaporizingcondensate. Also, weather data, e.g., a three day prediction ofnight-time and day-time temperature and insolation, could be supplied tothe controller by a telephone link and updated daily. The controllercould then determine the daily optimal operating conditions for theheating or cooling cycle, taking into account the cost of electricalbooster heating, the cost of using electrical backup energy, andopportunities to exploit mild night-time conditions to accumulatecondensate for subsequent more severe weather.

Adsorbent/Absorbate Pair Selection

In its broadest aspects, the invention is unlimited as to the particularfunctional adsorbent material and adsorbate (refrigerant) employed. Infact, it is contemplated that in an appropriate case anabsorbent/absorbate pair may be used. However, adsorption is preferredover absorption for the following reasons.

1. In the transfer of refrigerant from one vessel to another, withadsorption, only one substance is transported. In absorption systems,e.g., ammonia/water or sulfur dioxide/water, the refrigerant alwaystravels as a binary vapor. Eventually, the accumulation of absorbentmaterial in the evaporator (chamber II) becomes so large that itunderminds the operation of the device. Thus, the absorbent must beperiodically drained from the evaporator and returned to the absorber(chamber I). While it is obvious that provision could be made forautomatically conducting this step, it is a nuisance and is notnecessary in an adsorption system.

2. Adsorption is intrinsically a very rapid process. Given adequaterates of transfer of heat and vapor in the adsorbent material bed, thenet speed of adsorption is very rapid. This facilitates control andpermits certain steps, such as the rapid flash evaporation required inthe present cycle, which would be more difficult to carry out withabsorption.

3. The heat of adsorption of a vapor on a solid is very large, usually30-50% greater than the heat of vaporization of the liquid at the sametemperature. This is highly advantageous in the design of a chemicalheat pump because the net efficiency of the device increases as theratio of the heat of adsorption to the heat capacity of the deviceincreases. Stated differently, as much solar energy as possible shouldbe utilized in the system to drive chemical effects and as little aspossible absorbed as sensible heat.

4. Since adsorbent materials adsorb vapor at pressures which are muchlower than the equilibrium pressure of the vapor above its own liquid orsolid phase, adsorption systems permit ordinary liquids (e.g. water) tobe reduced to very low pressures and temperatures. For example, the useof adsorption enables water to be employed as a working refrigerant forrelatively low temperature refrigeration. This in turn allows ice to beformed by flash evaporation and results in heat storage both as heat ofcondensation and heat of fusion.

5. Adsorption, being generally a low pressure process, simplifies thedesign of chambers I and II for safety. This is a most significantconsideration in product engineering and packaging since it results inimplosion on failure. The silica gel/water based adsorption cyclediscussed above operates at pressures in the vicinity of 1-2 in. Hg.This is even lower than the pressure necessary to pump fluid through acollector to collect heat in conventional solar systems.

While silica gel/water systems are the only ones discussed in detailherein, it is obvious that other adsorbent/adsorbate pairs can be usedto advantage. Thermodynamic analysis of the cycle indicates that theselection of a particular pair should be based on a balancing of thefollowing criteria, employing the weather conditions in the area inwhich the system will be used as a background.

The adsorbent/adsorbate pair should have a high capacity to adsorb. Thisis because the higher the capacity to adsorb, the greater will be theheat storage capacity. The pair should also have a heat of adsorptionwhich declines rapidly with increased temperature. This enables the hightemperature solar heat to desorb large amounts of vapor. The adsorbentmaterial itself should have a low specific heat; sensible heat stored inthe adsorbent, although recoverable, detracts from the efficiency ofboth the heating and cooling cycles. The adsorbate should have a highheat of vaporization. This permits the cycle to receive large quantitiesof heat at low temperature during the crucial process D'-A. Further, theselected adsorbent/adsorbate pair should have adsorption characteristicssufficient to permit the reequilibration of the system in stage D'-A tobe self-sustaining. To achieve this goal, the heat of adsorption atmoderate temperatures (in the vicinity of 100° F.) should be fairlylarge.

The refrigerant should also have saturation properties which wouldminimize the mass of liquid which must be vaporized in the flash coolingprocess. This requires that the change of enthalapy on vaporization belarge compared with the change in enthalpy of saturated liquid over thedesired range of temperature depression. This is desirable because thevapor which must be flashed during stage D-D' readsorbs in chamber I,and therefore limits the amount of refrigerant which can be readsorbedduring stage D'-A. Lastly, it would be highly advantageous to select anadsorbent/adsorbate pair for which the isobars have very low slopes sothat large changes in the concentration of adsorbed gas can be effectedalong isobars for only moderate changes in temperature. This alsoincreases the capacity of the system to receive heat during the laststage of the cycle.

From the foregoing it should be apparent that a variety of differentadsorbent/adsorbate pairs can be used as desired. No single pair will befound which satisfies all of the foregoing requirements; any pairactually employed will accordingly represent a compromise. The use towhich the particular system is to be put, i.e., whether the unit will beused primarily for cooling or primarily for heating or more or lessequally for both will necessarily affect this decision. Accordingly,adsorbent/adsorbate pairs such as silica gel/water, silica gel/sulfurdioxide, charcoal/sulfur dioxide, silver chloride/ammonia, and othersmay be used. Furthermore, it is contemplated that mixtures of two ormore adsorbent materials and two or more adsorbates can be employed.

Modular Unit Embodying the System

As noted above, the storage of sensible heat in the system detracts fromits performance. Thus, in the ideal, it would be preferable to have allheat stored as chemical effects such as adsorption or condensation andnone as sensible heat. Accordingly, one important design criterion forany apparatus embodying the system is that it have a low internal heatcapacity. Also, in conventional solar powered systems, the parts of theoverall system are made by different manufactures and assembled orinstalled by different contractors. This complicates coordination of theconstruction and raises questions regarding who has the responsibilityfor ongoing maintenance and repair of the system. In view of this, animportant design consideration for any apparatus embodying the inventionis that it be sealed and self contained, amenable to mass production,and capable of being installed in units of varying capacity to suitvarious climatic conditions and buildings having different heating andcooling requirements.

In accordance with the invention, these goals are achieved if theapparatus described above is embodied as a modular unit, a number ofwhich are combined to provide a given capacity. In addition to acting asboth a heating and air conditioning device (or a refrigeration device),such a unit has inherent thermal storage and a build-in back-up energysource. Further, it serves as a solar collector and is made primarilyfrom low cost materials such as glass. The unit can be factory built,tested, and shipped ready for connection to a power supply and ductsystem.

Referring to FIG. 13, one such modular unit embodying the invention isshown. It comprises an elongated tubular glass enclosure 100 defining apair of chambers 102, 104, which, respectively, correspond to chambers Iand II in FIGS. 1-11. The chambers are separated by a valve 10 which isactuated by a remotely controlled electromechanical solenoid 106.Chamber 102 is surrounded by a coaxially arranged glass tube 108. Theannular space 110 is evacuated to minimize loss of heat by conduction ordiffusion from chamber 102. The exterior surface 112 of chamber 102 iscoated with a radiation absorptive material, and its interior is packedwith adsorbent material 103, preferably silica gel. Temperature andpressure sensors 80, 82 are disposed respectively in chambers 102, 104.Chamber 102 also contains an electrical resistance back up heater 120.Leads for all electronic components enter through electrical lead-in122. Chamber 104 is lined with an insulating material 114.

Ducts 116, 118 together double as a mounting for the unit and serve toprovide thermal communication between the contents of tube 100 andoutdoor or indoor air, as required. Duct 116 is placed in thermalcommunication with the adsorbent material 103 in chamber 102 by means ofa heat exchanging loop 123 for circulating heat carrying fluid. The loophas a heat conducting structure disposed within chamber 102 of a naturehereinafter described, but here only schematically illustrated at 124. Aseries of fins 126 disposed within duct 116 serve as a heat exchangesurface. Optionally, the loop includes a circulation pump 128.

Thermal communication between chamber 104 and duct 118 is established bymeans of a heat conducting structure 130 comprising a series of fins 132disposed to contact air passing through duct 118 and a series ofcup-like structures 134 for holding condensate. Fins 132 and structures134 are made of copper or the like and are in thermal communication.

The mounting and cooperative relationship of a plurality of the modularunits shown in FIG. 13 are illustrated in FIGS. 14 and 15. Preferably, aplurality of units arranged as a panel 135 are mounted on a base 136with the central axes 138 of respective units in parallel and ducts 116,118 connected in series. Ducts 116, 118 lead respectively to plenums140, 142 which are connected in parallel with other plenums of identicaldesign on other panels. One or more baffle systems (not shown) are usedto direct either indoor or outdoor air as required along ducts 116, 118at various stages of the cycle. A panel such as that depicted in FIG. 14will have a certain minimum heating and cooling capacity. Accordingly,the number of such panels necessary to provide the space heating and/orcooling requirements of a given building structure located in a givengeographical area can readily be calculated.

According to an important aspect of the invention, the panel includes acurvelinear diffuse light deflector 144 having plural specularreflecting surfaces 146 corresponding in cross-section to a segment of acylinder positioned at the opposite side of the collector tube from thesun. This system improves the efficiency of total energy collectionwithout tracking the sun or focusing the reflected radiation.Preferably, the tubes are no more than three diameters apart and thecylindrical reflector has its focal line within chamber 102. The radiusof curvature of the reflector surface exceeds the radius of the tube andis defined as a function of the tube diameter and tube spacing. Furtherparticulars concerning the construction and spatial relationship ofreflector 144 and double-walled tubular solar energy collectors aredisclosed in U.S. Pat. No. 4,091,796 filed Aug. 16, 1976, entitled"Solar Energy Collection Apparatus", the disclosure of which isincorporated herein by reference.

Each modular unit 145 is capable of effecting both the heating andcooling cycle as described above. Briefly, the vapor pressure in chamberI is raised and desorption of vapor powered by solar radiation 148absorbed by coating 112. With a stream of air passing through duct 118and with valve 10 open, refrigerant vapor (preferably water) desorbs,passes through the valve, and is condensed in cup structures 134, itsheat of condensation being removed via fins 132 and delivered as warmair to the interior of the building. When insolation ceases, valve 10 isclosed, pump 128 is actuated to circulate cooling fluid e.g.,fluorocarbon refrigerant, through cooling loop 124, and air is passedalong duct 116. When sufficient heat has been removed from chamber 102through the cooling loop to lower the refrigerant vapor pressure to adesired level, with no air passing through duct 118 (so that chamber 104is isolated), solenoid 106 opens valve 10. The aqueous condensate in cupstructures 134 undergoes flash evaporation and is thereby frozen. Heatof adsorption generated as the refrigerant readsorbs into silica geladsorbent 103 during flash evaporation is removed through duct 116 andused to heat the building. Next, outdoor air is passed through duct 118and is cooled as it gives up heat through fins 132 to the ice containedin cup structures 134 to provide heat of sublimation. The vapor thenmigrates through the valve 10 and is adsorbed, its heat of condensationbeing removed through cooling loop 122. By varying the rate at whichcooling fluid is passed through loop 122 and/or by varying the volume ofair circulated about fins 126 in duct 116, the vapor pressure withinchamber 102 can be maintained at a substantially constant level duringreadsorption of the refrigerant vapor. If, during latter portions of thelast stage of the cycle, booster heating is required to maintain thetemperature of the incoming air, such heating can be accomplished with abooster heater downstream of duct 116 and plenium 140 (not shown).

From the foregoing it can be appreciated that individual modular units145 can be mass produced, factory tested, and assembled into panels suchas those depicted in FIG. 14. A plurality of panels when connected tothe forced hot air system of a building, or, if a pipe system weresubstituted for the duct system illustrated, the forced hot water systemof a building, can provide all necessary heating and coolingrequirements.

Advantageously, the units efficiently collect sunlight and have only oneor two moving parts. Valve 10 and its actuating mechanism cannot bedispensed with. However, pump 128 of cooling loop 122 may not berequired unless it is desired to utilize the constant vapor pressurereadsorption feature of the process of the invention. In any event, itwill be possible to controllably exchange heat with adsorbent material103 merely by varying the quantity of air passed through duct 116 andover fins 126.

Another significant advantage of the modular unit described above isthat it is adaptable for use with various adsorbent/adsorbate pairswhich, per unit volume of adsorbent material, require varying quantitiesof heat to desorb the refrigerant. For example, a solar collectorcomprising a pair of coaxilly arranged tubes and an evacuated annularspace is commercially available under the trademark SUNPAC from OwensIllinois Corp. This tube has a 1.75 inch inside diameter and is 48inches long. Its interior volume is 6.68×10⁻² ft³. Assuming that it ispossible to fill 85% of this volume with adsorbent material,approximately 2.55 pounds of silica gel could be placed in the tube.This mass of silica gel, saturated with water, can be completelydesorbed with 452 BTU of insolation. However, the SUNPAC tube is capableof collecting 1000 BTU per day or more. Its solar energy adsorptivity ismaximized by the use of the diffuse light reflector and other noveldesign features, but is ultimately a function of the surface area of theinner tube, e.g., the surface area of tube 100.

In order to gain full advantage of the heat pump cycle disclosed here,it is necessary to increase the ratio of the capacities for adsorptionto solar collection. For a tubular collector, this ratio goes as theratio of interior volume to surface area and so behaves as the diameterof the tube. Thus, by using a larger diameter tube it is possible tomatch the capacities as required or to build in long term storage. Forexample, with a six inch inside diameter tube 48 inches long, it ispossible to provide for energy storage of approximately 2.9 days ofsolar exposure within the system if silica gel is the adsorbent ofchoice. A tube of these dimensions can hold about 49 pounds of silicagel, which can use about 8620 BTU of energy. The tube will be able tocollect about 3000 BTU solar heat per day. Thus, if no heat wererequired in the building during night-time, it would take 2.9 daysbefore all the water was desorbed.

This type of storage is not directly comparable to storage of solarenergy by other means such as thermal reservoirs. Specifically, storagein a conventional thermal reservoir (e.g. a tank of water) has as itsfirst purpose to provide night-time heating. The system described abovehas this capability even when the amount of heat necessary to desorb allthe gel is equal to one day's collecting capacity. The basic idea oflong term storage (e.g., for more than one 24 hour period) is to collectinsolation that is not needed in mild weather and to store it for use inmore severe weather. In order to have this capability, the system musthave the capacity to collect surplus solar energy. A collector tubewith, for example, a capacity of 3 days worth of storage can actuallystore 3 days worth of solar energy if its condensate is not used duringthe night. Thus, simply by varying the diameter of the tube, it ispossible to vary the ratio of the area of radiation absorptive surface(and thus solar energy absorption capacity) to the volume of the chamber(and thus the total amount of heat needed to desorb the gel) to achieveadvantages. In any case the diameter should be no less than thatnecessary to result in efficient use of all solar heat collected.Preferably, the diameter is such that long term storage of the typediscussed above is provided. When adsorbent materials other than silicagel are used, chamber 102 can nevertheless be readily sized inaccordance with these teachings.

Heat and Mass Transfer Considerations

Proper operation of the foregoing apparatus depends upon the device'sability to carry out both heat and mass transfer at high rates. Analysisindicates that the rate limiting process in the cycle is internal heattransfer into and out of the adsorbent material. This heat transferoccurs by thermal diffusion, and thus the important property of theadsorbent is its thermal diffusivity α. Diffusion distance D, over whicha disturbance will travel into a medium by diffusion in time t is givenby the formula: ##EQU1## The significance of this distance is that if achange in temperature occurs in the boundary of a mass of silica gel ofthickness h, and then when enough time elapses for the diffusiondistance D to be approximately between h and 2h, the transient heattransfer will have become essentially complete. For silica gel,α=84×10⁻⁴ ft² /hr: in five minutes, D=0.32 inches; in 10 minutes, D=0.45inches; and in 15 minutes D=0.55 inches. If silica gel is the adsorbentof choice, it should be packed in chamber 102 in layers approximately1/4 to 1/2 inch thick with each layer having access to a heat transfersurface of material of high thermal conductivity such as copper. Withthis design, it is possible to complete transient heat transfer throughthe silica gel to a thermal conductor in about 10-12 minutes. This timeframe allows the various dynamic changes in the system to take placerapidly and results in an easily controlled, responsive device. Whenusing other adsorbent materials of thermal diffusivity αft² /hr, thedistance D between any point within the adsorbent material to a sheet ofheat conducting material should therefore be ≦√0.2α (i.e., 12 minutesdiffusion time) even more preferably, D≦√0.12α.

Within the range of vapor pressures and concentrations that occur in thecycles described, the transport of vapor into and out of the adsorbentbed occurs by diffusion. The rate of diffusion is the rate limiting stepin the overall mass process, as the process of adsorption itself isinstaneous compared with vapor migration. For transient diffusion ofvapor in silica gel, the diffusivity of the gel α_(v) =2.96 ft² /hr.Given that distance Δ=√α_(v) t, it can be seen that for silica gel,vapor will diffuse 6 inches in about 5 minutes, and will diffuse aboutthree inches in 1.27 minutes. Accordingly, if the adsorbent material isarranged in chamber 102 such that vapor does not have to travel morethan about 3 inches, the transient time for mass diffusion will beapproximately 11/4 minutes: mass diffusion taking place about 4 times asrapidly as thermal diffusion. For other adsorbent materials having avapor diffusivity α_(v), the distance Δ between any point therein to avapor flow path should be ≦√0.2α_(v). Mass diffusion from the adsorbentmaterial to a vapor flow path will thus be complete in no more thanabout 12 minutes, and thermal and mass diffusion occur in about the sameamounts of time. Preferably, Δ≦√0.033α_(v).

One structure which can achieve the foregoing dimensional requirementsin the environment of chamber 102 of the modular unit depicted in FIG.13 is set forth in FIG. 16-18. The adsorbent material is packaged asthin wafers between which thinner copper discs or sheets are placed. Atleast one edge of the wafer is exposed to a vapor flow path. Such awafer, depicted in FIG. 18, has a thickness T no greater than 2√0.2α,where α is the thermal diffusivity of the adsorbent material in ft² /hr.For silica gel, T is no greater than about one inch. Heat can thereforediffuse from any point within the wafer to a copper or other thermalconducting sheet material in contact with the wafer sides within about12 minutes. The height H of the wafer, for adsorbent material of vapordiffusivity α_(v) ft² /hr, should be no greater than about 2√0.2α_(v),where both the top 150 and bottom 152 are in communication with a vaporflow path. If a vapor flow path is disposed at surface 150 only (bottomsurface 152 terminates in a wall), then the height H should be nogreater than √0.2α_(v) so that mass diffusion from any point inadsorbent material wafer to the vapor flow path adjacent surface 150 iscomplete within about 12 minutes. For the silica gel/water system, H ispreferably ≦3 inches.

Referring to FIG. 16 and 17, a preferred heat conducting structure foruse in chamber 102 of the modular unit of FIG. 13 is depicted. Thestructure consists of a can 154 comprising a cylindrical casing 156traversed by a plurality of heat conducting separators or fins 158which, in combination with the casing 156, define a plurality of wells160. Each well holds a wafer of adsorbent material such as that shown inFIG. 18. The bottom of the can is closed. The outer surface of casing156 is blackened to facilitate reception of heat from the walls 112 ofthe collector tube. The interior surface 162 of collector tube 112 iscoated with a high emissivity material.

The can 154 has a plurality of cooling tubes 164 which serve the dualpurposes of providing a channel for the circulation of fluid(schematically depicted in FIG. 13 as portion 124 of closed heatexchanging loop 122) and serving as connectors between cans axiallyarranged within chamber 102. As shown, each tube has a femalefrusto-conical section 166 and a male frusto-conical section 168disposed at its opposite ends. The male and female sections sealinglyinterfit as illustrated in FIG. 17 to form four continuous channels. Thecooling tubes are themselves made of copper or the like and are in goodthermal contact with fins 158 and casing 156. It may be advantageous toemploy a wire gauze 172, or other similar material, intermediate stackedcans 154, to give the unit further structural strength.

Male and female interfitting conical sections 166, 168, when fittedtogether as shown in FIG. 17, together comprise axial separating meanswhich separate adjacent cans thereby to define a radical vapor flow path170 between the cans. Further, female conical section 166 extendsradially out from casing 156, and serves as a radial spacer forseparating cans 154 from the interior surface 162 of tube 100. Thus, anannular space 174 defined between the outside surfaces of casings 156 ofcans 154 and the interior surface of tube 100. The space extends axiallyalong the tube, and serves as an axial vapor flow path.

In operation, thermal diffusion can occur from any point within theadsorbent material wafer to a heat conducting fin 158 at least withinabout 12 minutes. Mass diffusion of vapor, even from a point adjacentthe bottom portion 152 of the wafers of the adsorbent material up to avapor flow path 170, occurs in much less time. Vapor can thus migratealong radial flow paths 170 to axial flow path 174, and to the valve 10of the molular unit. Also, heat can be removed from the adsorbentmaterial by heat carrying fluid circulating along cooling tubes 164. Ofcourse, the cooling tubes in the can adjacent the end of chamber 102would be altered so that a closed loop is formed.

One of the barriers to exploiting the phenomenon of sublimation of icebelow the triple point for low temperature refrigeration with water isthe diffusion of heat into the ice. Thermal diffusion in ice isrelatively slow compared with other heat transfer processes usingconventional refrigeration. The thermal diffusivity of ice, α_(ice), isequal to 4.45×10⁻² ft² /hr. Thus, if the ice is kept to about 1/2 inchdepth, the time required to diffuse a thermal disturbance through itwill be about 5.8 minutes. This time is comparable to the time requiredfor thermal diffusion in silica gel in wafers dimensioned as set forthabove. For other adsorbates of thermal diffusivity α_(c), the distancebetween a wall of the container holding the condensate and all pointswithin the condensate should be ≦√0.2α_(c), preferably √0.12α_(c). Inthe modular unit disclosed in FIG. 13, these design features areembodied as a plurality of cup-like containers 134 made of heatconducting material such as copper which are coupled directly to fins132. Each of the discrete containers 134 are open to the chamber 104 andthus the free flow of vapor is assured.

Sublimation of the ice, or volatilization of other refrigerants, and theheat transfer from the gel adsorbent material occur simultaneously inthe respective chambers during any given stage of the cycle. In thisprocess, both the sublimation and the extraction of heat from the silicagel are subject to external control. The net effect is that the responsetime of the system will be the longer of the response times of the twophenomena rather than the sum of these times. Accordingly, the thermaldiffusion in the silica gel remains the rate limiting phenomenon in theoperation of the system.

Uses and Modifications

From the foregoing discussion, it should be apparent that, withoutdeparting from the spirit and scope of the invention, many modificationscan be made in the cycle itself, in the methods of exploiting theheating and/or cooling capacity of the cycle, in the degree of controlto which the cycle can be subjected, in the nature of the apparatus inwhich the cycle takes place, and in the uses to which such a system canbe put.

Thus, the cycle may be optimized for use in various climates by, forexample, selecting a particular adsorbent/adsorbate pair, usingintercooling with a cold air return stream during certain portions ofthe cycle, and taking other similar steps that will be apparent to thoseskilled in the art.

As mentioned above, various means for storing the cooling capacitygenerated in the system for use during periods of intense insolation, inaddition to those set forth specifically above, will also be possible.

Some of the more important variations in the basic cycle involve controlof various process steps to optimize thermodynamic efficiency. Thus, inchamber I, as noted above, vapor pressure can be regulated bycontrolling heat transfer so that adsorption and desorption occur at orclose to constant vapor pressure, e.g., along lines R(B-C) and O(D'-A)of FIG. 12. In this way, the thermodynamic processes in the cycle occurefficiently under more or less reversible conditions. Another example ofthis aspect of the invention involves control of the valve 10 during orprior to stage D'-A so that the temperature of the condensed refrigerantin chamber II, and thus the temperature of evaporation, is maintainedjust slightly below (e.g., 10° F.) the then current temperature of theatmosphere. In this way, the temperature of evaporation can bemaintained at optimal values relative to what will often be a changingatmosphere temperature. Also, during warm nighttime weather, valve 10may be controlled to allow only so much vapor into chamber I as isneeded to release the small amount of heat necessary to maintain theindoor temperature. Thus, condensate is conserved for use in future,more severe weather.

An apparatus for conducting the cycle need not necessarily take the formof the modular unit disclosed herein. In fact, in particular situationsit may not necessarily be advantageous to exploit the system in modularform.

The primary focus of the foregoing discussion has been on space heatingand cooling requirements. However, it is obvious that the system may beadapted without the exercise of invention to a variety of otherapplications. Nonlimiting examples include a building having arefrigerated section and a heated section. In this case, heat could beextracted from the refrigerated section while remaining portions of thebuilding were supplied with heat. This could be accomplished in a singlecycle merely by suitable redirecting air streams. Heat extracted fromthe refrigerated section not needed to maintain the temperature of theremainder of the building could be rejected to outside air; heat neededin excess of that removed from the refrigerated section to warm thebuilding could be extracted from outside air. Another exemplary use forthe process and apparatus of the invention is in providing refrigeratingcapacity for ocean going vessels such as fishing vessels. In thisapplication, heat could advantageously be rejected directly into therelatively cold ocean water. It may also be useful to equip chamber IIwith an additional adsorption reservoir so that some of the heat ofvaporization of the working fluid could be stored, rather than beingtransferred to the thermal sink to be warmed.

In attempting to build staged mechanical heat pumps to transfer heatover very large temperature differentials (for example 250° F.), it isordinarily necessary to use multiple compressors, multiple heatexchangers, etc., all of which compound costs and maintenance. Theintermittent chemical cycle disclosed herein offers a unique advantagefor staging with very simple hardware as compared with mechanicaldevices. Thus, staging can be obtained as shown in FIG. 19 wherein theevaporator/condensor chamber II of a first system or stage 200 is builtinto the adsorber/desorber chamber I of a second system 202. Thus, thesilica gel/water system described above could be directly coupled to asecond system using, for example, silica gel and ethanol, for extractingheat from very low temperatures. Alternatively, it could be coupled tosome other adsorbent/adsorbate system for delivering heat at very hightemperatures. The coupling in this case would require only that theappropriate chamber of one system be immersed in its complementaryvessel in the other system.

In the system depicted in FIG. 19, solar heat is used to desorb vapor inchamber I and the vapor is condensed in chamber II as usual. The heat ofcondensation of the vapor desorbs another vapor contained inadsorber/desorber chamber I in system 202, and that vapor is in turncondensed at low temperature in chamber II. When the process isreversed, the liquid (or solid) phase in chamber II' would receive heatfrom a low temperature reservoir, and the heat of readsorptionultimately generated in chamber I of system 200 would be delivered tothe reservoir in which heat is desired. Such a staged system has certainpractical advantages for additional storage, operation in very severeclimates, or possibly for industrial heating.

Other embodiments are within the following claims.

What is claimed is:
 1. Apparatus powered primarily by solar radiationfor heating space in a building, said apparatus being operable to effectan intermittent heat pump cycle employing an adsorbent material and aworking refrigerant comprising a condensible adsorbate, said apparatuscomprisingfirst and second sealed chambers separated by a valve which,when open, provides a refrigerant vapor transfer path between thechambers, said first chamber containing an adsorbent material, having aclosed loop heat exchange system for exchanging heat with said adsorbentmaterial, and being in thermal communication with a solar collector,said second chamber being serviced by a second heat exchanger, whereinsaid first chamber includes a heat and mass transfer promoting structurecomprising a plurality of discreet wafers of adsorbent material forfacilitating heat and mass transfer during adsorption/desorption, eachsaid wafer having a surface exposed to a vapor flow path and a surfacein contact with a sheet of material having high thermal conductance,said sheets being in thermal communication with said closed loop.
 2. Theapparatus of claim 1 wherein said adsorbent material has a thermaldiffusivity of α ft² /hr. and a vapor diffusivity of α_(v) ft² /hr., andsaid wafers are dimensioned such that:(a) the distance D between anypoint therein to a sheet of thermal conducting material is no greaterthan √0.2α, whereby transient heat transfer from the adsorbent materialto the sheet material is complete within about 12 minutes; (b) thedistance Δ between any point therein to a vapor flow path in no greaterthan √0.2α_(v), whereby mass diffusion from any point in the adsorbentmaterial to the vapor flow path is complete within about 12 minutes. 3.The apparatus of claim 2 wherein the adsorbent material is silica geland the adsorbate is water and wherein D≦0.45 inch and Δ≦3.0 inches. 4.The apparatus of claim 2 wherein D≦√0.12α and Δ≦√0.033α_(v).
 5. Theapparatus of claim 1 wherein said first chamber comprises a tube, andsaid heat and mass transfer promoting structure comprises a plurality ofcylindrical, sheet metal cans arranged coaxially within said tube,saidcans having outside casings radially separated from the interior surfaceof said tube and axially separated from each other, each said canhaving:an axial dimension no greater than √0.2α_(v) ; and a plurality ofsubstantially parallel sheet metal separators connected to said outsidecasing, the distance between said separators being no greater than2√0.2α.
 6. The apparatus of claim 5 wherein the axial dimension of eachsaid can is no greater than about √0.033α_(v) and the distance betweensaid separators is no greater than 2√0.12α.
 7. The apparatus of claim 5wherein each said can has at least two cooling tube segments in thermalcommunication with a sheet separator and respective segments in adjacentcans have interfitting male and female connectors, said segmentstogether comprising a portion of said closed loop within said firstchamber.
 8. The apparatus of claim 7 wherein each said can has axialextensions beyond said outside casing to provide spacers for axiallyseparating said cans.
 9. The apparatus of claim 7 wherein each said canhas radial extensions to provide spacers for radially separating saidcasing from the interior wall of said tube.
 10. The apparatus of claim 4wherein the interior surface of said tube comprises a high emissivitymaterial and the exterior surface of said outside casing is coated witha radiation absorptive material.
 11. The apparatus of claim 1 having thefurther improvement wherein a heat transfer-promoting condensate holdingstructure is disposed within said second chamber, said structurecomprising:a plurality of discrete containers of heat conduting materialin said second chamber for holding nonvapor refrigerant and promotingheat transfer therewithin, each said container being open to theinterior of said chamber and being in thermal communication with saidsecond heat exchanger.
 12. The apparatus of claim 11 wherein saidnonvapor refrigerant has a thermal diffusivity α_(c) ft² /hr and whereineach said container is dimensioned such that the distance L between awall of said container and all points therewithin is no greater than√0.2α_(c).
 13. The apparatus of claim 11 wherein L≦√0.12α_(c).